The present invention relates to a cooling device of a water-cooled engine and a method of manufacturing the same, and in particular, to a cooling device of a water-cooled engine and a method of manufacturing the same, in which plural cylinders are arranged in line, and a cylinder head with cross-flow type of intake-and-exhaust arrangement includes intake port portions and exhaust port portions which connect to respective combustion chambers and an exhaust collective portion where the exhaust port portions are collected.
In general, an exhaust manifold connects to exhaust ports of a cylinder head outside the cylinder head. Meanwhile, the structure in which inside the cylinder head are formed the exhaust port portions connecting to respective combustion chambers and the exhaust collective portion where the exhaust port portions are collected has been recently proposed aiming at omitting the exhaust manifold, as disclosed in Japanese Patent Laid-Open Publication No. 2000-205043.
In the structure disclosed in the above-described patent document, the exhaust port portions and the exhaust collective portion are formed inside the cylinder head as described above. In this case, the high-temperature exhaust gas may give a large thermal load to the cylinder head. Accordingly, the water jacket may be necessary to cool the cylinder head. Herein, according to the structure disclosed in the above-described patent document, the water jacket is formed to surround the exhaust port portions and the exhaust collective portion. Specifically, the water jackets which are positioned above and below the exhaust port portions and the exhaust collective portion and the water jacket which extends vertically to connect these water jackets are formed inside the cylinder head. The water jacket extending vertically is provided between two exhaust port portions provided at each cylinder and has a shape along these exhaust port portions.
However, since the water jacket surrounds the exhaust port portions and the exhaust collective portion in the above-described structure, there is a problem in that the exhaust gas may be cooled too much improperly.
That is, it is preferable that the exhaust-gas temperature do not increase too high from a perspective of the cylinder head's reliability. From an exhaust-gas treatment standpoint, meanwhile, the high temperature of the exhaust gas is preferable, so it may be needed for the cooling water inside the water jacket not to cool the exhaust port portions and the like excessively.